1. Technical Field
The present invention relates to a stereo signal processing circuit which decodes an L+R signal and an L−R signal from a received signal and obtains an L signal and an R signal by applying addition or subtraction between the L+R signal and the L−R signal.
2. Background Art
In a radio receiver, a predetermined reference signal which is determined according to a frequency of a desired station is mixed so that a signal from the desired station is converted into an intermediate frequency (IF) signal and a desired station signal is extracted from the IF signal.
In order to efficiently replay an audio signal, a wide band AGC (Automatic Gain Control) for attenuating the received signal when a signal level of the received signal is greater than a predetermined level and a narrow band AGC for attenuating the level of the received signal when the level of the extracted desired station signal is greater than or equal to a predetermined level are also provided.
There exist certain circuits which have a tuning circuit, and obtain the IF signal after a signal in a range near the desired station signal is extracted. In this case, the wide band AGC is operated according to the signal level after tuning.
In FM broadcasting, stereo broadcasting is employed. In this case, a main signal (L+R signal) and a sub signal (L−R signal) are transmitted, and the receiver adds the L+R signal and the L−R signal to obtain the L signal and subtracts the L−R signal from the L+R signal to obtain the R signal, to replay the stereo signal.
In such a stereo replay, when the signal level of the narrow band signal is reduced, an SN (signal-to-noise) ratio is degraded. Therefore, in such a case, the replay is sometimes switched to monophonic replay in which the signal is replayed only from the main signal.
Related art documents of the present invention include JP S61-69231 A and JP 2009-152873 A.
In the radio receiver, there may be cases where the signal of the desired station cannot be sufficiently received due to adjacent interference. Therefore, there is a desire to more suitably receive the signals in such a case.